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Discussion Starter · #1 ·
2001 Mitsubishi Eclipse GT V6 3.0 l

I have looked for similar posts, but none are exactly like this.

Only when the engine is cold, the car starts bogging down and hesitating while driving. The idle is perfectly fine, however. Once the engine is warm/hot the problem completely disappears.

I replaced the IAC, new spark Plugs and wires, cleaned intake and throttle body, new temp sending unit, new distributer cap, cleaned EGR valve, new crankshaft position sensor, new timing belt, new waterpump, bank 1 o2 sensor tests good, no vacuum leaks from smoke test, MAF sensor cleaned.

Previous owner says computer may be going bad. Any other answers beside the computer are appriciated. Unless you are sure that is the only thing left. I do have codes for the o2 sensor that was tested good, as well as codes for the crankshaft position sensor. Some banks are rich while the opposite are lean. No causes could be found by mechanic.

Please help!
 

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There are a couple things I can think of that may or may not help. First being, have you unplugged your battery for like 5 minutes and reset your ecu? It will take a few minutes to relearn idle procedures and what not; I'm assuming you did this at some point in your list of replacements but I didn't see it specifically noted. Second thing is, have you double checked each of your vacuum lines? I've had a similar issue with my car since I got it and I know the vacuum lines are all messed up, simply get a little spray bottle from the dollar store and fill it with some soapy water and spray it around the lines while the car is running and if you see more bubbles it means you've got a leak.

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Discussion Starter · #3 ·
yes i have tried resetting the ecu that way, but it didnt work. all vacuum lines were tested using smoke and spray by a mechanic. Keep in mind this ONLY happens when cold and is fine when hot or running temp
 

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try replacing the pcv valve ($5) and replace both upstream o2 sensors since they dictate fuel/air ratio...double check the vac hoses by the egr...outside chance it could be fuel pump, but not likely based on symptons. Check for dirty air filter, too.
if no luck, then it could be the ecu since you've replaced pretty much everything else at this point.
 

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First, why do you have a CEL for the crankshaft position sensor. I think you need to fix that regardless, and it might also be causing your hesitation problem.

Sounds like you have a problem with your air/fuel ratio that causes the engine to hesitate when operating in open loop. Once you warm up and start closed loop, your short term fuel trims compensate enough to make the engine run smooth(er). I'm not an expert with fuel trim, but I think a closer analysis of whether each of your LTFT and STFT are rich or lean will help you narrow this down.

For example, you might have a faulty injector stuck open and adding too much fuel, making the engine hesitate at idle. Or the MAF is dirty and thinks there's more air than there really is so you end up with a too-rich AFR. When you reach operating temp the STFT kicks in and helps lean the mixture out (which would show a max lean STFT). Again, I'm a newb at understanding fuel trims but I think the trims are what you should look at. It won't tell you the exact component, but it can help you narrow down the underlying problem.

Also, what CEL code are you getting for your O2 sensor? Is it one of P0171 through P0175, indicating you're running too lean or too rich?
 

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Discussion Starter · #6 ·
try replacing the pcv valve ($5) and replace both upstream o2 sensors since they dictate fuel/air ratio...double check the vac hoses by the egr...outside chance it could be fuel pump, but not likely based on symptons. Check for dirty air filter, too.
if no luck, then it could be the ecu since you've replaced pretty much everything else at this point.
First, why do you have a CEL for the crankshaft position sensor. I think you need to fix that regardless, and it might also be causing your hesitation problem.

Sounds like you have a problem with your air/fuel ratio that causes the engine to hesitate when operating in open loop. Once you warm up and start closed loop, your short term fuel trims compensate enough to make the engine run smooth(er). I'm not an expert with fuel trim, but I think a closer analysis of whether each of your LTFT and STFT are rich or lean will help you narrow this down.

For example, you might have a faulty injector stuck open and adding too much fuel, making the engine hesitate at idle. Or the MAF is dirty and thinks there's more air than there really is so you end up with a too-rich AFR. When you reach operating temp the STFT kicks in and helps lean the mixture out (which would show a max lean STFT). Again, I'm a newb at understanding fuel trims but I think the trims are what you should look at. It won't tell you the exact component, but it can help you narrow down the underlying problem.

Also, what CEL code are you getting for your O2 sensor? Is it one of P0171 through P0175, indicating you're running too lean or too rich?
I dont know why the CEL shows a crankshaft failure, but that sensor has already been replaced and tested by a mechanic. Also if it was bad, a mechanic said the car wouldnt start. The MAF has already been cleaned. And the o2 sensor is the bank 1 sensor 1 i believe. I can check which codes it has and which banks are lean and which are rich as i have a sheet from the mechanic. Also a smoke test has been done and a test to check the o2 sensor that came up as bad. Both results showed the o2 sensor in question is still good and no vacuum leaks.
 

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Discussion Starter · #7 ·
I dont know why the CEL shows a crankshaft failure, but that sensor has already been replaced and tested by a mechanic. Also if it was bad, a mechanic said the car wouldnt start. The MAF has already been cleaned. And the o2 sensor is the bank 1 sensor 1 i believe. I can check which codes it has and which banks are lean and which are rich as i have a sheet from the mechanic. Also a smoke test has been done and a test to check the o2 sensor that came up as bad. Both results showed the o2 sensor in question is still good and no vacuum leaks.
most everything has been cleaned or replaced. Check original post
 

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Discussion Starter · #8 ·
Check engine codes are as follows: P0171(lean bank 1), P0175 (rich bank 2), P0134 and P0154, P0335, P0340.

Propane on bank 1 sensor 1 responds well.
Crankshaft positon sensor checked to work fine.
Smoke test reveals no vacuum leaks.
Bank 1 very lean.
Bank 2 slightly rich.

These are the comments from my mechanic.
 

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P0335 and P0340 together are often the distributor. The P0134 and P0154 indicate both upstream O2 sensors are worn out and need to be replaced, or there's a wiring problem on the sensors.

Unless you have reason to think the PO fiddled with the ECM, I think it's unlikely that its bad. It's much more likely that you need new o2 sensors and a distributor.

I'd start with the O2 sensors though and see what happens. They're not intended to last forever, so worst case is you're changing them a little early. Plus they're much cheaper than a new distributor.
 

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Discussion Starter · #10 ·
P0335 and P0340 together are often the distributor. The P0134 and P0154 indicate both upstream O2 sensors are worn out and need to be replaced, or there's a wiring problem on the sensors.

Unless you have reason to think the PO fiddled with the ECM, I think it's unlikely that its bad. It's much more likely that you need new o2 sensors and a distributor.

I'd start with the O2 sensors though and see what happens. They're not intended to last forever, so worst case is you're changing them a little early. Plus they're much cheaper than a new distributor.
Maybe, however it still doesn't sound like it would cause ONLY cold engine hesitation while maintaining a good idle. I believe the distributor was already replaced as well as atleast 1 of the o2 sensors. Looks like the one on the top front where there the headers are.
 

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I'm not a trained mechanic and I don't know everything, but I'm pretty familiar with the cars I own. Mostly from working on them, but also from looking critically at peoples' posts over the years and sifting out the good responses from the well-intentioned but inaccurate ones.

Having codes for both the crankshaft and camshaft position sensor points to a problem with your distributor and fits your symptoms of P0335 and P0340 and an engine that still runs. You can find lots of examples of this. Sure, something else could be generating the P0335 and P0340 codes. But this is the most likely problem IMO for your cam and crank CELs. Replacing the distributor might not have anything to do with your hesitating engine. But the CELs are a clear sign that something is wrong with your ignition system, and your ignition system can impact things like hesitation. I agree that the distributor should impact engine performance over all temperatures, but you ought to fix it regardless. If your mechanic already replaced it, he may have used a non-OEM part that doesn't work quite right, or bent a pin on a connector, or the new crank position sensor may be aftermarket and generating a funny signal. It could also be something in the wiring harness that connects to the distributor. Who knows? The fact is you're getting codes that shouldn't be there, so something is wrong. And it might just fix your hesitation.

Your other codes all indicate there's an underlying problem with your air/fuel ratio due to your LTFT settings being off. Maybe they're off because there's an intake leak, or an exhaust leak, or a bad fuel injector. Maybe they're off because your oxygen sensors aren't working quite correctly. Regardless, when the engine is warm the STFT are able to correct it and the engine runs well because the problem of an incorrect AFR is being masked. The fact that one bank is rich and the other is lean points to an air or fuel problem after the intake plenum. There are a lot of things upstream of the plenum (MAF, air temp sensor, coolant temp sensor, throttle body, TPS, fuel pump, fuel pressure regulator, manifold pressure sensor) that could impact your AFR, but I would expect them to make both banks too rich or too lean. Again, not sure exactly how this causes hesitation unless your mixture is really rich, but it looks to me like this is a problem. And it might just fix your hesitation.
 

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2001 Mitsubishi Eclipse GT V6 3.0 l

I have looked for similar posts, but none are exactly like this.

Only when the engine is cold, the car starts bogging down and hesitating while driving. The idle is perfectly fine, however. Once the engine is warm/hot the problem completely disappears.

I replaced the IAC, new spark Plugs and wires, cleaned intake and throttle body, new temp sending unit, new distributer cap, cleaned EGR valve, new crankshaft position sensor, new timing belt, new waterpump, bank 1 o2 sensor tests good, no vacuum leaks from smoke test, MAF sensor cleaned.

Previous owner says computer may be going bad. Any other answers beside the computer are appriciated. Unless you are sure that is the only thing left. I do have codes for the o2 sensor that was tested good, as well as codes for the crankshaft position sensor. Some banks are rich while the opposite are lean. No causes could be found by mechanic.

Please help!
Have you checked the ignition coils and check the spark going to the sparkplugs due to not burning all of the fuel which can be caused by oil in the sparkplug holes or the ignition spark grounding out. Is the value cover gasket leaking because this can cause some of these issues? Did you use an OEM crankshaft or camshaft sensor?
 

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Discussion Starter · #13 ·
Have you checked the ignition coils and check the spark going to the sparkplugs due to not burning all of the fuel which can be caused by oil in the sparkplug holes or the ignition spark grounding out. Is the value cover gasket leaking because this can cause some of these issues? Did you use an OEM crankshaft or camshaft sensor?
No ignition coils, but the previous owner had a mechanic replace the distributor. I dont know if it is oem or not. Multiple mechanics told me that it wouldnt even run or even if it it, it wouldnt run as good as it does if something was wrong with the crankshaft sensor. The crankshaft sensor was replaced. Also we just replaced the valve cover gaskets, both of them. Also the intake manifold gaskets. I just checked the PCV valve and it works fine, i also cleaned it. No oil on the spark plugs or very minimal since we replaced it. New spark plugs and spark plug wires. It does burn oil and my tailpipe is black. Do not know if that has anything to do with each other. i hear a weird *put *put sound that is only noticable inside the car where it sounds like it is coming from under the car. Dont know if that is connected. like i said smoke test shows good. gas test shows o2 sensors good. I do have a record sheet of the test that one shop did with all values at the time of codes if you want that. I am so stumped on this. It also feels like it is losing power overall such as less horsepower.
 

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No ignition coils, but the previous owner had a mechanic replace the distributor. I dont know if it is oem or not. Multiple mechanics told me that it wouldnt even run or even if it it, it wouldnt run as good as it does if something was wrong with the crankshaft sensor. The crankshaft sensor was replaced. Also we just replaced the valve cover gaskets, both of them. Also the intake manifold gaskets. I just checked the PCV valve and it works fine, i also cleaned it. No oil on the spark plugs or very minimal since we replaced it. New spark plugs and spark plug wires. It does burn oil and my tailpipe is black. Do not know if that has anything to do with each other. i hear a weird *put *put sound that is only noticable inside the car where it sounds like it is coming from under the car. Dont know if that is connected. like i said smoke test shows good. gas test shows o2 sensors good. I do have a record sheet of the test that one shop did with all values at the time of codes if you want that. I am so stumped on this. It also feels like it is losing power overall such as less horsepower.
Depending on how many miles are on the vehicle, the catalytic converter could be plugged, so rev up the motor while someone checks the airflow out of the exhaust pipe. Are the spark plugs clean and white or burnt and black after running the vehicle for 50 miles? Did you do a compression check of the cylinders? Loss of horsepower and burning oil points to rings letting oil passed them.
 

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Discussion Starter · #15 ·
Depending on how many miles are on the vehicle, the catalytic converter could be plugged, so rev up the motor while someone checks the airflow out of the exhaust pipe. Are the spark plugs clean and white or burnt and black after running the vehicle for 50 miles? Did you do a compression check of the cylinders? Loss of horsepower and burning oil points to rings letting oil passed them.
there are 250+k miles and i just replaced the spark plugs. the previous ones were clean. you may be right that the rings are starting to wear, and the catalytic converter could be clogged especially with all the black smoke. But could either of those cause open loop problems?
 

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there are 250+k miles and i just replaced the spark plugs. the previous ones were clean. you may be right that the rings are starting to wear, and the catalytic converter could be clogged especially with all the black smoke. But could either of those cause open loop problems?
The catalytic converter being plugged would cause motor issues until it warms up and the rattling noise could be from inside the cat. It will cause a loss of power due to no air flow out of the pipe.
 

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Discussion Starter · #17 ·
The catalytic converter being plugged would cause motor issues until it warms up and the rattling noise could be from inside the cat. It will cause a loss of power due to no air flow out of the pipe.
its more of a glug* glug*/put* put* sound. But that sounds like probably my next best bet. Since the o2 sensors have been replaced, then i have a feeling the cat could be clogged. Thanks! I will post whatever i find
 
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